You have a condition called "sulphur water". It is not all that uncommon and while pretty stinky it is not harmful. It especially occurs with the RV's hot water tsnk.
I have had this in my system a couple of times. The first time I got it I completely cleaned out my water system and this was a lot of work.
The second time I got it I replaced my water filter that I used for the city water supply. I also use a filter when filling the fresh water tank too.
The last thing I do when the rig is in storage is empty the hot water tank (do this after it cools or it could be dangerous).
If you want to do the water treatment method you'll need hours to do this since it involves getting a diluted bleach solution from the fresh water tank into all the plumbing, then letting it sit for several hours (some recommend overnight). The last step is then to evacuate the bleach which can take a while since all faucets must eventually be opened and run for a while to remove the bleach. I hope you realize you might want to be at a dump station or campground or you might overfill your gray tanks.
Do an internet search of "stinky water" or "sulfur water" and you should find plenty of articles on what it is, and how to fix it. I learned prevention is the best medicine - good water source, very good filtration, and don't let water sit for long periods of time even when you think it's clean and pure.
